A droplet actuator typically includes one or more substrates configured to form a surface or gap for conducting droplet operations. The one or more substrates establish a droplet operations surface or gap for conducting droplet operations and may also include electrodes arranged to conduct the droplet operations. The droplet operations substrate or the gap between the substrates may be coated or filled with a filler fluid that is immiscible with the liquid that forms the droplets.
Droplet actuators are used in a variety of applications, including molecular diagnostic assays, such as enzymatic assays. In one application, enzymatic assays are used as part of a routine testing process to test newborn infants for various genetic disorders. For example, enzymatic assays may be used to test for deficiencies in glucose-6-phosphate dehydrogenase (G6PD) activity. Currently, the most commonly used enzymatic assay for G6PD deficiency is a rapid qualitative fluorescent spot test detecting the generation of NADPH from NADP. The test is positive if the blood spot fails to fluoresce under ultraviolet light, i.e., there is marked deficiency or lack of G6PD enzyme activity when no fluorescence is observed. However, this assay is a qualitative assay that requires highly trained personnel to visually “read” the sample for fluorescence or lack of fluorescence. Therefore, there is a need for new approaches to G6PD deficiency testing that is less prone to error and that is more readily available.